Created Date: April 06,2004

Created by: MikeW

Currently installing my first AD PLC, a 450, on a test facility. Initially it will be connected to it's own PC until it is fully commisioned including tuning 4 PID loops and 3 proportional loops. A twin brother to this facility is due to go on line a month after the first one is running. I would like to share the same PC for a HMI since there will be minimal need for operator to interface through the HMI once they are debugged. Longer term, additional units may be added, not sure if they would be 405 series or I possibly could get by with 205s.

Question 1:

As I view the options, it looks like they are:

Ethernet using the open slot that is available on the existing bases.

Using existing serial ports and have a slower RS 422 network.

Is there another option I'm unaware of that can be done?

Question 2:

Is a 422 network "fast enough " to handle a HMI that will be accessing multiple PLCs? e.g. how fast of an update would you expect: Refresh at 10 Hz, 1 Hz, or 0.1 Hz or less?

Question3:

What would be the limitation on the number of PLCs to be hung on the network/ HMI from a practical standpoint? RS422 allows 32 connections and Ethernet in the hundreds, I should have no more than 25 total PLCs.

Question 4:

Any known problems using either option? I plan to route the cabling in conduit with some other low level signal cable so electrical noise should be minimized.

TIA for your help getting me up to speed on networking options as I have been out of this type of work for the last 8 years.

Created Date: April 06,2004

Created by: marksji

I'm not really all that familiar with RS422, but I 've got alot of experiance with the ECOM modules in the 205's.

1) Modbus would also be an option, I think.

2) Someone else should probably answer this, but realistically how fast do you need? Are 1 second updates fast enough?

3) The ECOM modules are limited to 63 devices if using module ID to identify the different PLCs because of their addressing method. There are other identity methods, but module ID gives you the most flexibility, this shouldn't be a problem since you only want ~25 PLCs connected anyway.

4) If you go with ethernet do not use the cheap off the shelf network switches from best buy / compusa... You need a switch with broadcast storm protection, preferably an industrial switch. Broadcast storm protection will make sure that every device on the network gets a chance to "talk " even if there is a whole lot of traffic generated by a couple of devices. Remember that by nature ethernet does not guarentee timely communication.

If it were me I'd go with ethernet because of the future ease of expansion and virtually limitless cable length (repeaters and fiber if needed). Its really easy to add a network cable and PLC to an existing ethernet network. You can also plug in your notebook and access all the PLCs easily via ethernet, or throw up wireless bridges where wire is difficult to run.